Exokernel

An exokernel, also referred to as a vertically -structured operating system is a type of kernel, and thus the central part of an operating system. In contrast to most other kernel, it provides very little abstraction of the hardware for programs and is limited to prevent resource conflicts and to check access rights.

Exokernels can be thought of as a logical continuation of the microkernel concept. In contrast to this, they are still more rigid in the choice of mechanisms provided.

History

The concept of a Exokernels existed since 1994, but was used (until 2005) only from the Massachusetts Institute of Technology (MIT ) for several systems, including Exos. Another concept named Nemesis has been developed by the Universities of Cambridge and Glasgow, Cisco Systems, and the Swedish Institute of Computer Science.

Function

Most kernel hide the computer's hardware by a hardware abstraction layer from the software. So it is with virtual memory, for example, possible to allocate memory for a program, but the exact memory address can not be set.

Exokernel however, are limited to as few abstractions as possible. They allow programs to directly access memory blocks, disk slices, etc. This freedom can be used to speed up programs by eliminating unnecessary abstractions (and intermediate layers ) can be omitted. The task of Exokernels it is to determine whether the requested resource is free, so there is no resource conflict, and whether they may also be used by the respective program.

Libraries

Abstractions are provided in an exokernel operating system outside the kernel through a system of libraries ( Library), similar to those of conventional operating systems, however, limited, are flexible by nature of the Exokernels. So it is - at least theoretically - possible to run different operating systems such as Windows or Unix on a Exokernel by using each of them different libraries.

Monolithic kernel | Hybrid kernel | microkernel | Exokernel